On the go and no time to finish that story right now? Your News is the place for you to save content to read later from any device. Register with us and content you save will appear here so you can access them to read later.

WASHINGTON - Security jitters on land, sea and air marked the anniversary of the September 11 attacks, but a heightened state of alert around the world allowed a sombre day of remembrance to pass largely undisturbed.

United States embassies or consulates in Germany, Denmark, Italy and Luxembourg received letters containing white powder, sparking fears of an anthrax attack. Checks were still being made on some of the substances but powder contained in a letter to the consulate in Hamburg turned out to be sugar.

With the help of fighter jets, missiles, sniffer dogs and patrols, commemorations passed off peacefully in New York and Washington, the two cities scarred by the attacks that killed 3025 people one year ago - as they did in other countries expressing their sympathy.

With the US placed on the second-highest state of security alert - code orange - the nation's airports were quiet. Fewer planes took to the skies and many more air marshals were on duty, but the day was not without incident.

A Northwest Airlines jetliner with 99 passengers and crew on a flight from Memphis to Las Vegas diverted to Arkansas after crew grew concerned when four passengers performed what appeared to be a "cleansing ritual" on board. The plane landed safely and the four were questioned by authorities.

Later, an American Airlines jetliner returned to Houston because passengers thought they saw a person with a weapon.

The Fokker 100 jet with 50 passengers on board was escorted to the airport by two F-16s, and two suspects were taken into custody, but investigators found no weapons.

Every corner of New York seemed guarded by police, National Guard, federal agents, armed teams of special officers, snipers, dog patrols and bioterrorism units. Fighter jets patrolled overhead, while US Navy ships monitored the harbours.

A Government building in Columbus, Ohio, was evacuated after a sniffer dog detected possible explosives in a vehicle left parked outside, police said. The person who drove the vehicle was seen leaving on foot and is being held for questioning.

The US Coast Guard ordered a Liberian flag freighter out to sea off the coast of New Jersey after it found low traces of radiation on board.

The US' closest ally, Britain, erected a wall of security before memorial services in London and imposed a no-fly zone over the city and over nuclear power and military installations.

In Germany, a passenger who spent too long in an aircraft toilet prompted a security alert and a full search of the Lufthansa plane, the airline said in Berlin.

German police launched a dawn raid on a mosque in Hamburg, the city where some of the suicide hijackers once lived, after a tip-off about a possible first-anniversary bomb.

In the one serious clash reported, police in Pakistan killed two gunmen and arrested five in a shootout with suspected members of Osama bin Laden's al Qaeda network, the presumed perpetrators of last year's carnage.

Pakistan police said they arrested five suspected militants who had allegedly planned to bomb American fast-food chains in southern Pakistan.

Attacks on three US bases in Afghanistan caused no injury or damage but highlighted continued instability, 11 months after US forces attacked the al Qaeda network there and drove its backers, the Islamist Taleban movement, from power.

Some US embassies served as focal points for scattered protests in Asia.

Philippine troops with machine-guns guarded the US Embassy as anti-American protesters, waving flowers, marked the anniversary with a plea to Washington to avoid war with Iraq.

The British Embassy in the Philippines was evacuated and closed for the day after an anonymous phone call saying a bomb had been placed in the building.

US forces in the Middle East were put on highest alert.

Iraq said it was also tightening security at key facilities - but in its case, against a US attack.

Attacks on three US bases in Afghanistan caused no injury or damage but highlighted continued instability, 11 months after US forces attacked the al Qaeda network there and drove its backers, the Islamist Taleban movement, from power.

About two dozen US embassies and consulates were shut, either for security or to let staff attend memorial ceremonies. Both the United States and Britain closed their embassies in Indonesia, the world's most populous Muslim nation, and in Pakistan.